Food dehydrators are often round, but there are a few rectangular ones also. Nesco is one of the more common manuafacturers and there are a number of models. Nearly all have four or more plastic food trays that can be stacked. Most have a fan in the top to circulate air, and there is a heater to keep the air hot. Some have thermostatic control, so you can set the temperature that you want. Since the food trays are optimized for small pieces of damp food, you need some non-stick sheets in case you want to dehydrate a sauce. Most of these have a power consumption of 500 watts to 1000 watts. The big ones tend to take up more space in the kitchen, and the small ones are more economical. One trick to proper use is to slice the food very uniformly.